(1) Field of the Invention:
The present invention relates to a gas stream blower of a non-contact type tonometer in which a compressed air stream is blown upon an eye to be examined to deform a cornea of the eye, a physical amount indicative of this deformation and a pressure of the fluid are detected, and an eye pressure is determined from the correlation between the physical amount and the fluid pressure.
(2) Prior Art Statement:
For instance, an apparatus shown in FIG. 4 has been heretofore known as a gas stream blower for the non-contact type tonometer of this kind.
According to this gas stream blower, an arm 2 of a rotary solenoid 1 is connected to a piston rod 4 integrated with piston 3 and a compression chamber 6 of a cylinder 5 in which the piston 3 is arranged to communicated with a nozzle 7. The axis of this nozzle is directed to an eye-examining position. This apparatus is so designed that when electric current is passed through the rotary solenoid 1, the arm 2 is turned clockwise, while when electric current is cut, the arm 2 is returned to its original state by means of a spring force of a spring (not shown). At the lower portion of the cylinder 5 is formed an air escape hole 8 for escaping air from the compression chamber 6 at a compression initial stage.
In such a construction, when the arm 2 is turned clockwise by actuating the rotary solenoid 1, the piston 3 is displaced upwardly through the piston rod 4. Thereby, the pressure in the compression chamber 6 becomes higher, so that air in the compression chamber 6 is blown upon the eye 9 to be examined at the eye-examining position from the nozzle 7.
At this time, the change rate of the moving speed of the piston 3 is large at the actuating initial stage of the rotary solenoid 1, that is, at the time of the compression starting. Thus, if no air escape hole 8 is provided in the cylinder 5, the pressure in the compression chamber 6 varies in a curve fashion at the time of the compression starting as in an a portion of a pressure-varying line A in FIG. 5. However, when the air escape hole 8 is provided in the cylinder 5, air in the compression chamber 6 escapes to the outside through the air escape hole 8 at the compression start initial stage. Consequently, the pressure in the compression chamber 6 linearly varies at the time of compression starting as in a pressure-varying line B of FIG. 6.
Therefore, when the gas stream blower shown in FIG. 4 is used, the air stream of which pressure linearly varies can be blown upon the eye to be examined through the nozzle 7.
However, such a gas stream blower has the following disadvantages:
(1) In this gas stream blower, when electric current to the rotary solenoid 1 is cut after the air stream is blown upon the eye 9 to be examined, the rotary solenoid 1 is returned to its original state by a spring force of the spring not shown and the piston 3 is displaced downwardly. Thereby, the pressure in the compression chamber 6 lowers, so that air near the eye 9 to be examined is sucked into the compression chamber 6 through the nozzle 7. Thus, air which is sucked into the compression chamber 6 at the air-sucking time is blown upon an eye of a next person to be examined.
However, when air stream is blown upon the eye 9 to be examined in such a manner, tear is scattered from the eye 9 to be examined, so that the scattered tear is sucked into the compression chamber 6 through the nozzle 7 after the air blowing and is blown upon the eye to be examined of the next person. Hence, such is not hygienically favorable.
(2) Further, since the piston 3 is driven by the rotary solenoid 1 provided with the arm 2 in the above-mentioned gas stream blower, the rotary solenoid 1 is arranged on the side of the cylinder 5. Therefore, the gas stream blower becomes larger in the horizontal direction, which is not favorable in making the whole apparatus compact.
(3) In addition, since the cylinder 5 and the nozzle 7 are rigidly and integrally combined through an objective lens L, vibrations of the rotary solenoid 1 at the time of compression are transmitted to the nozzle. However, when the vibrations are transmitted to the nozzle 7, a position where air stream is blown upon the eye 9 to be examined is deviated, so that there occurs a problem that accurate measurement is impossible.
(4) Moreover, in order that the change in the pressure of the air stream blown upon the eye 9 to be examined may be linearly done, the air escape hole 8 has been conventionally provided. Thus, when the air escape hole 8 is communicated with the compression chamber 6 by downwardly displacing the piston 3 as mentioned above and the piston 3 is further downwardly displaced, contaminated air in the exterior is sucked into the compression chamber 6. Consequently, this contaminated air is blown upon the eye to be examined, which is not hygienically favorable.